For the uninitiated, Signal rolls secure text messaging and encrypted voice-over IP calls into a single package that works as a full-fledged SMS replacement app. Kept afloat by community donations and grants, Signal for iOS and Android is free and does not contain ads. The Android version is one of our Editors' Choice winners for secure messaging apps.

The news comes as Apple is fighting a recent court order that directs the company to create a new mobile operating system that can thwart iPhone encryption to help the FBI break into a handset owned by one of the San Bernardino shooters. The company on Thursday urged a California court to vacate the order, saying the request is unprecedented, puts iPhone users at risk, and will inevitably lead to similar requests from law enforcement agencies around the country.

"No court has ever authorized what the government now seeks, no law supports such unlimited and sweeping use of the judicial process, and the Constitution forbids it," Apple said in a filing.

Also this week, the New York Timesreportedthat Apple is developing new security measures that make it impossible for the government to crack a locked iPhone. Cupertino is also eyeing stronger encryption of customers' iCloud backups, the Financial Times said, citing anonymous sources familiar with the company's plans.

For more, check out PCMag's full reviews of Signal for iPhone and Android.